Fossils and Geologic Time
 _________________ are the remains or traces of _____________________________. They are important
components of __________________and ______________________ rocks.
 The___________________________________ that is formed is determined by the
____________________ under which an organism died and __________________________
 ___________________________: • Some remains of organisms—such as teeth, bones, and shells—may
not have been altered, or may have changed hardly at all over time.
 Conditions Favoring Preservation
• Two conditions are important for preservation: _____________________ and the
________________________ of hard parts.
Petrified fossils:
Molds and casts:
Carbon films:
Preserved Remains:
Trace Fossils:
The principle of ________________________________________ states that fossil organisms succeed one
another in a _________________ and ____________________ order. Therefore, any time period can be
recognized by its fossil content.
____________________________________ are widespread geographically, are limited to a __________
span of geologic time, and occur in ____________________.
Geologic Time Scale
Based on their interpretations of the rock record, geologists have divided
______________________________ history into units that represent ___________________ amounts of
time. Taken together, these time spans make up the ______________________________.
_________________ represent the ____________________ expanses of time. Eons are divided into
__________. Each era is subdivided into _________________. Finally, periods are divided into smaller units
called ________________.
There are three eras within the Phanerozoic eon:
the ________________________, which means “______________________,”
the _______________________, which means “______________________,” and the
________________________, which means “______________________”
Each period within an era is characterized by somewhat ______________________________changes in life
forms as compared with the changes that occur during an era.
The periods of the Cenozoic era are divided into still smaller units called ___________________, during
which even _______________________ changes in life forms occur.
During Precambrian time, there were ____________________________. These life forms are more difficult
to identify and the rocks have been ________________________________.
*Precambrian: _____________of earth’s history, fossil records very
_________________, ______________ rock record
A sedimentary rock may contain particles that contain ___________________________________, but these
particles are __________________ the same age as the rock in which they occur.
The age of a particular mineral in a _____________________________________ does not necessarily
represent the time when the rock was _____________________. Instead, the date may indicate when the
rock was __________________________